Protective device.



D. T. MAY.

PROTECTIVE DEVICE.

APPLICATION FILED MAY25|19IL Patented Deal?, I918.

muy

ernten SDAVS ri'. MAY, 0F NEW* YORK, N. Y., ASSIGNOB TO WESTERN ELECTRIC COll'llPANEL?,` NCRPORATED, NEW YGRK, N. Y.,A CGRPORATION OF NEW-YORK.

LPRTECTEVE DEVICE.

assises.

v Speciiication of Letters Patent.

I'ilatented Dec. i7, 1918.

Application filed May 5, i917. Serial No. 'oli.

To @El whom may concern:

Be it known that l, Darin T. liliana citizen of the United States, residing at New York, in the county oi New York and State of New York, have invented certain n` a' and useful improvements in Protective llevices, of which the following is a full, clear, concise, and exact description.

This invention relates to devices tecting' electrical circuits from the de, tive eilects of abnormal currents or impulses due to lightning` discharges, crosses 'with lines carrying high potential currents and other like causes, and more particularly it relates to an improvement suitable, forexn ample, for use in protective devices of the type commonly known as vacuum lightning arresters in which electrodes separated hy a. short gap are inc losed in al container e:-;- hausted to such a degree that the gap will break 'down and provide a discharffe path at a much lower 4voltage than it would ii placed in air at atmospheric pressure. There is, however, an objection to the vacuum type of arrester in that, following a loss or decrease in vacuuin, the degree oi protection afforded the line may he decreased to such an extent that protection will no longer he aiforded against the power and lighting circuits in common use.

To ohviate this defect, 'there has recently 'been proposed vacuuin type of arrester having, in addition to the main operating gap, an auxiliary gap which will offer 'a disehargepat". and provide protection 'to the line in case of decrease ci vacuum within the container. Such an arrester is shown and described in an application hy Stephenson,- Serial NolSQfliG. 1

rl`his auxiliary gap is so proportioned with respect to the main gap and the pressure wit-hin the container that discharge 'takes place only across the main gap, solong as'the` pressure remains constant. However,

with a decrease or loss oi vacuum, the auxiliary gap, because oit its shorter length, provides a discharge path which ailords pre-- tection to the circuit. has heen found, however, that even under conditions of satn isactory vacuum, tne discharge` will at times take place across the auxiliary-gap and in so doing increase the possibility of maintenance troubles.

lt is the object or" the present invention eliminate maintenance trouhles resulting .electrodes si and electrode 7 with electrode 5. suine a difference of potential to exist, tendicroin the discharge occasionally taking place across the. shorter gap under conditions of satisfactory vacuum within the container and to accomplish this result, there is provided a construction adapted to place across It has been found that f a slight neutralization is necessa'r i to At arcing at the. auxiliary gap under l conditions and this neutralization is ancient to prevent the functioning of the apparat-usas desired when the vacuum is impaired.

The several features of this invention may heinore clearly understood hy reference to the drawings, in which Figure l shows diagrammatic-ally the` means for providing a neutralizing field across the auxiliary gap, while Figi'. 2 shows one method oi" applying this construction to vacuum arresters of the two-gap type.

Referring more particularly to break down. onl

to Fig. 1, the and 5, separated by the main gap 6, are extended to lie outside of the electrodes 7 and 8 of the `auuiiliary gap 9. These electrodes 'are oppositely connected to the electrodes of the main gap, electrode S being joined electrically with electrode l lf we as'- ing to cause a discharge to take place across the main gap from electrode-l to electrode 5, there will also exist a tendency for discharge to take place'across the auxiliary gap from electrode 8 to electrode 7, as shown hy the arrow in full lines. However, thisrtendency is partially neutralized by the electrostatic iield existing between the extensions of the electrodes al and 5, this field being in the direction of the dotted arrow as shown.

ln Fig'. 2, is shown a vacuum arrester of the double-gap type, equipped with means for providing an opposing1 field across the auxiliary gap. The evacuated container l0 within which the electrodes are mounted, is preferably of glass, `formed and evacuated inthe usual manner and cemented to a suitalole hase ll. The electrodes l2 and 13 are two iiatpieces oi metal formed at one end in the manner shown, to provide the inain gap 11i across which Athe -discharge takes place under normal operating` conditions.

' The lower ends of these electrodes are bent ico p the leading-in Wires and 16. Located between the electrodes 12 and 13 from which they are separated by the insulating disks 17 and 18 are the electrodes 19- and 20. These electrodes are separated froinleach other. by

a disk of insulating material 21 somewhat larger in diameter than the electrodes and having at its center an opening 22 Which acts as the auxiliary air gap in case of den crease of vacuum. Placed on the outside of the electrodes 12 and 13 are the two insulating disks 23 and 24 and vbinding the 'whole assembly together are the meta-l straps ,245 Vand 26,.. which cross the electrodes and also -a` tendency "are secured 'at each end by a bolt, one of these boltsfbeing shown at 27. The electrode 12 is connected electrically to electrode 20 and lthe electrodel is`.connccted electrically to electrode 19. It 'will thus be seen that the same' relationship exists between the two sets of electrodes asis presented inthe arrangej ment shown diagrammatically in Fig. 1.

In case aidiierence of potential exists be'- tween the leading-in Wires 15 and 16 of a 'polarity tending to-cause 4a discharge to pass from-'electrode 12 to electrode 13,- there is for discharge to' take place across the smaller air gap from electrode 2 0 to electrode 19. This tendency, however, .is

to 'a certain extent neutralized by tie electrostatic fieldset up between the extensions of the electrodes 12'and 13. The desired strength of' this electrostatic, field is obtained by the'proper spacing of the electrodes.

What is claimed is: ,1. vIn a protective device, apairof electrodes soplaced that the spark-over voitage' is substantially a minimum, a second pair of electrodes so spaced that'the spark-over voltage iszhigherthan that of said first pair, and means -for partially neutralizing the electrostatic iield across said second pair of electrodes.

2.,In a protective device, an evacuated is higher than that of container, a pair of.electrodes so spaced therein that the spark-over voltage is substantially a minimum, a second pair ofelectrodes so spacedl'that the spark-over voltage the electrostatic eld across the shorter gap. fl. In a protective device, an evacuated container, a plurality of electrodes therein forming a main gap and anY auxiliary gap, the electrodes of saidA auxiliary gap being connected in opposite electrical relation to the electrodes or" said main gap, and so lo- ,gcated as to lie Within the electrostatic iield across the electrodes of said main gap.

5. In a protective device, an evacuated container, a plurality of electrodes providing a main gap and an auxiliary gap, electrodes of said auxiliary gap being positioned to produce an to that produced by the electrodes of said maingap.

6. In a protective device, an evacuated container, a. plurality of electrodes providing a main gap and an auxiliary gap, electrodes of said auxiliary gap being cross-connected to the electrodes oiV said main gap and so located With respect thereto that the electrostatic field produced by a d iiereiice of potential across said auxiliary gap is in opposition to that produced across the electrodes of said main gap.

In Witness whereof I hereunto subscribe my name this 22nd day of ay A. D., 1917.

DAVID T. MAY.

second pair of elecy electrostatic field in opposition 

